drm/i915/scatterlist: fix kernel-doc parameter documentation

drivers/gpu/drm/i915/i915_scatterlist.h:164: warning: Function parameter or member 'release' not described in 'i915_refct_sgt_ops'
drivers/gpu/drm/i915/i915_scatterlist.h:187: warning: Function parameter or member 'rsgt' not described in 'i915_refct_sgt_put'
drivers/gpu/drm/i915/i915_scatterlist.h:198: warning: Function parameter or member 'rsgt' not described in 'i915_refct_sgt_get'
drivers/gpu/drm/i915/i915_scatterlist.h:214: warning: Function parameter or member 'rsgt' not described in '__i915_refct_sgt_init'

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0b31edbb33116c8002dd1e72d3ad25efe5dd0176.1683041799.git.jani.nikula@intel.com